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Neutron Dose Assignment for K-25 and 

Portsmouth Gaseous Diffusion Plants

White Paper 

National Institute for Occupational

Safety and Health 

May 6, 2019

Matthew H. Smith, Elizabeth Algutifan, Michalene Rodriguez, 

Thomas R. LaBone, and Keith McCartney

Oak Ridge Associated Universities Team

Reviewed by Chuck Nelson and Tim Taulbee 

Division of Compensation Analysis and Support

This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution. 
White Paper Neutron Dose Assignment for K-25 and Portsmouth Gaseous 

Diffusion Plants

May 6, 2019

Page 2 of 24

This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution. 

INTRODUCTION

Neutron dose to workers at gaseous diffusion plants (GDP) has been an issue of concern because 

some workers were unmonitored or monitored for exposure to photon and beta radiation only. 

Information is provided on this topic in the U.S. Department of Energy (DOE) Guide of Good 

Practices for Occupational Radiological Protection in Uranium Facilities (DOE 2009), but the 

basis for the information in that document is limited. Therefore, this white paper focuses on 

measurements and calculations of the neutron dose and neutron-to-photon (N:P) ratio from 

various uranium compounds with an emphasis on exposures to highly enriched uranium (HEU) 

compounds at the K-25 and Portsmouth Gaseous Diffusion Plants. 

PURPOSE

The purpose of this white paper is to determine a reasonable N:P ratio that can be used to assign 

dose for GDP energy employees during periods when neutron dose data were not reliable, not 

available, or not recorded. For K-25, this time period consists of the era prior to 1992. In the 

case of Portsmouth, although limited neutron monitoring began in 1987, monitoring of all 

employees with the potential for neutron exposure did not occur until 1995. 

BACKGROUND

The interaction of alpha particles from uranium with nuclei of fluorine, oxygen, and other lowatomic weight atoms generates neutrons with energies of approximately 2 MeV (DOE 2009). 

The magnitude of the neutron flux varies based on total activity of the uranium (a function of 

enrichment) and the chemical compound (combining of uranium with fluorine or oxygen). In the 

case of UF6, the typically measured neutron dose equivalent rates for storage containers are as 

follows (DOE 2009): 

Natural uranium (NU) to 5% enriched uranium (EU): 0.01 to 0.2 mrem/hr 

Very highly enriched uranium (97%+): 2 to 4 mrem/hr (contact) 

1 to 2 mrem/hr (3 ft or 1 m) 

The potential for significant worker exposures to neutrons generated by (α,n) reactions in 

uranium compounds is not very high unless a worker spends a large amount of time near storage 

containers of uranium fluoride or uranium oxide compounds or in processing areas for large 

quantities of those materials (DOE 2009). At very high 235U enrichments, the N:P dose ratio can 

be as much as 2:1, and neutrons can be the limiting radiation source for whole-body exposure 

(DOE 2009). As stated previously, there is a significantly limited basis for this information from 

the DOE Guide of Good Practices for Occupational Radiological Protection in Uranium 

Facilities (DOE 2009). The N:P ratio of 2:1 should be considered an upper bound of the 

potential range of ratios seen in facilities handling HEU. The neutron doses from low-enriched 

235U compounds or from uranium metals are not limiting doses (DOE 2009). 
White Paper Neutron Dose Assignment for K-25 and Portsmouth Gaseous 

Diffusion Plants

May 6, 2019

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This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

The current technical basis documents for K-25 and Portsmouth Gaseous Diffusion Plants both 

recommend assignment of neutron dose (before 1997 at Portsmouth and for any era at K-25) 

using an N:P ratio of 0.20, based on survey data from the Paducah Gaseous Diffusion Plant 

(PGDP) discussed below. 

NEUTRON DATA DEVELOPMENT AND ANALYSIS

Studies have been published of measured neutron doses and N:P ratios near storage cylinders 

containing depleted uranium (DU), NU, low-enriched uranium (LEU), or HEU in the form of 

UF6 at the Paducah, Portsmouth, and K-25 Gaseous Diffusion Plants. In some cases, these 

studies focused on large (14-t) cylinders in outside storage yards, while others were 

measurements of smaller HEU storage cylinders inside the facilities. These studies include: 

• UF6 cylinder yard survey (Paducah)

• HEU storage cylinder dose rates (Portsmouth)

• HEU storage vault/storage cylinder measurements (Portsmouth)

• Area monitoring: neutron and photon dose measurements (Portsmouth)

• Personnel monitoring: neutron and photon dose measurements (Portsmouth)

• Neutron dose rate survey results (K-25)

• Neutron and photon dose rate modeling for cylinder yards (K-25)

• Neutron and photon survey data area and area monitoring results (K-25)

• Personnel monitoring: neutron and photon dose measurements (K-25)

• Static dosimetry measurements (Y-12 Plant)

• Neutron and photon survey data (Y-12 Plant)

• Personnel monitoring: neutron and photon measurements (Y-12 Plant)

Paducah

At the Paducah plant, measurements during a UF6 cylinder painting project in the cylinder 

storage yard gave values for N:P dose ratios ranging from 0.14 to 0.42 with an approximate 

average of 0.2 (BJC 1999). These cylinders, however, contained either DU or NU. 

Portsmouth

Neutron Dose Rate Data

Cardarelli (1997) quotes values for measurements of the neutron dose near small (5-inch 

diameter) HEU storage containers that ranged from 3.0 mrem/hr (contact) to <0.5 mrem/hr (at 1 

meter). These values are in reasonably good agreement with the values in the DOE Guide of 

Good Practices for Occupational Radiological Protection in Uranium Facilities (DOE 2009). 

This report also cites the neutron dose component of total external dose as 12.5% based on a 

monitoring study of uranium material handlers in 1995. It is important to note that this study 

included workers exposed to a variety of uranium enrichments. 
White Paper Neutron Dose Assignment for K-25 and Portsmouth Gaseous 

Diffusion Plants

May 6, 2019

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This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution. 

In 1992, measurements taken in the product withdrawal (PW) vault (Building X-326) at 

Portsmouth indicated a neutron dose rate of 0.8 mrem/hr at a distance of 0.6 to 1.3 m facing a 

group of HEU cylinders (Soldat and Tanner 1992). Another survey was conducted in 1995 of a 

single 5A cylinder (97% HEU) in the X-345 Building. The recorded neutron dose rates at that 

time were 2.1 mrem/hr and 0.77 mrem/hr at distances of 15.2 cm and 30.5 cm, respectively 

(Scherpelz and Murphy 1995). Unfortunately, photon measurements were not made in either of 

these two studies. 

Neutron and photon rate measurements were documented in a 1986 memo for four empty and six 

full 5-inch product cylinders stored in the X-326 PW vaults. Surface neutron and photon dose 

rates for the empty cylinders were ≤ 0.5 mrem/hr and ≤ 1.0 mR/hr, respectively (N:P ratio = 0.5). 

Neutron and photon dose rates for the full cylinders were ≤ 3.0 mrem/h and ≤ 2.4 mR/hr, 

respectively (N:P ratio = 1.25). At a distance of 1.0 meter, the combined neutron and photon 

dose rate was 0.2 mrem/h for empty cylinders and 0.5 mrem/hr for full cylinders (Bassett 1986). 

N:P Ratio Data from Area Monitoring Measurements

A summary memorandum from 2008 provides annual Portsmouth area dosimetry data that were 

collected to meet the requirements of Dosimetry Program Standards (PGDP 2002). Outdoor 

annual neutron and photon dose measurements for the period 2004 to 2008 were available for the 

following radiological facilities: X-326, X-330, X-333, X-342, X-343 X-344, X-530, X-705, X710, and X-745. Data were also provided for nonradiological facility areas as well as Perimeter 

Road near the cylinder yards. Paired positive photon and neutron measurements were recorded 

at the following facilities/areas: X-330, X-344, X-343, X-530, X-745, and Perimeter Road near 

the cylinder yards. The average N:P ratio derived from this data was 0.147 ± 0.09 with a 

minimum value of 0.01 and a maximum value of 0.398 (McGuire 2008). 

N:P Ratio Data from Employee Dosimetry Measurements (1992 to 2013) 

Four databases containing historical dosimetry records for Portsmouth Gaseous Diffusion Plant 

employees were reviewed in order to calculate a claimant-favorable N:P ratio. The databases 

reviewed are as follows: 

• 3_Individual_Dose_Ports (overlaps with REMS_Portsmouth 1992–2013 Exp Recs 

database)

• Extra_REIRS_Ports (overlaps with 3_Individual_Dose_Ports database) 

• REIRS_Portsmouth 1992–2013 Exp Recs

• REMS_Portsmouth 1992–2013 Exp Recs 

The Portsmouth Radiation Exposure Information and Reporting System (REIRS) database was 

not useful in calculating an N:P ratio because no neutron dose records were included. In 

addition, as indicated above, two of the databases were actually subsets of other databases. 

Thus, only the 1992 to 2013 Radiation Exposure Monitoring System (REMS) database was used. 

Positive paired neutron and photon doses from this database were used to calculate a claimant-
White Paper Neutron Dose Assignment for K-25 and Portsmouth Gaseous 

Diffusion Plants

May 6, 2019

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This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution. 

favorable N:P ratio that can be applied to certain workers in facilities where enriched uranium 

was handled. It should be noted that positive neutron results appeared in the REMS database 

beginning in 1999 (Bechtel Jacobs era). 

Evaluation of REMS_Portsmouth 1992–2013 Exp Recs Database

A total of 38,964 records are contained in the Portsmouth REMS database. These encompass the 

period 1992 to 2013. A review of these records reveals the following information: 

• A total of 10,721 unique individuals were monitored by external dosimetry during this 

period. 

• Of the 10,721 individuals monitored, 722 were also monitored for neutrons (7%) at one 

time or another. 

• This database indicates that neutron monitoring began at Portsmouth in 1996, although 

the hard copy records in the NIOSH Division of Compensation Analysis and Support 

Claimant Tracking System (NOCTS) indicate an earlier date: 

o 1987 – sporadic monitoring for a few individuals 

o Fall 2005 – widespread monitoring

• It should be noted that United States Enrichment Corporation (USEC) dosimetry records 

began to be included in a separate database beginning in 1997 (REIRS). 

• Of the 722 individuals monitored for neutrons, 56 had at least one neutron monitoring 

result that exceeded the neutron limits of detection (LOD) of 10 mrem. 

• Positive neutron results do not appear in the REMS database until 1999. Health Physics 

Records System printouts in NOCTS, however, indicate positive neutron dose as early as 

1987 for one individual (PGDP date unknown). 

• USEC personnel wore a combined thermoluminescent dosimeter (TLD). 

• DOE personnel wore an albedo neutron dosimeter separate from their regular issued 

TLD. 

Table 1 shows a breakdown of monitored individuals by year, based on a review of the REMS 

database. 
White Paper Neutron Dose Assignment for K-25 and Portsmouth Gaseous 

Diffusion Plants

May 6, 2019

Page 6 of 24

This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution. 

Table 1. Portsmouth employee dosimetry data (1992–2013). 

Year # Individuals Monitored for Total External 

Dose

# Individuals Monitored for Neutron Dose 

(ND)

1992 3,628 0

1993 3,589 0

1994 4,404 0

1995 4,485 0

1996 3,957 444 (all ND)

1997a 144 0

1998 176 4 (all ND)

1999 204 36

2000 421 30

2001 639 32

2002 640 39

2003 541 26

2004 650 25

2005 643 64

2006 762 40

2007 731 31

2008 803 33

2009 1,219 95

2010 1,544 144

2011 2,718 142

2012 2,737 184

2013 2,662 147

Source: Portsmouth REMS Database 1992–2013.

a. Databases split in 1997; beginning in 1997, the REIRS database contains all USEC employees but no neutron 

monitoring results. 

Development of N:P Ratio Based on Portsmouth Dosimetry Data

A total of 161 records in the REMS database indicate neutron dose values greater than the LOD 

of 10 mrem. These values were divided by their paired photon dose values to calculate an N:P 

ratio for each line of data. These ratios were then averaged to obtain an overall N:P ratio. If a 

positive neutron dose had a corresponding photon dose of less than its LOD of 10 mrem, the 

photon dose was set equal to 10 mrem. This occurred with 10 records. In addition, a doubling of 

the radiation weighting factor from 10 to 20 was accounted for beginning in 2010. Based on this 

approach, the average N:P ratio was calculated to be 0.369. 
White Paper Neutron Dose Assignment for K-25 and Portsmouth Gaseous 

Diffusion Plants

May 6, 2019

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This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

K-25

Neutron Dose Rate Data

Discussions of N:P ratio values were found in a variety of documents written to address 

radiological safety issues associated with the K-25 cylinder storage yards. In a May 2000 report, 

an N:P ratio of 0.25 was cited, with the notation that many of the neutron dose rate 

measurements were zero (BJC 2000). A final safety analysis report (FSAR) for the K-25 

cylinder yards, written in 1997, indicated contact dose rate values between 1 and 6 mrem/hr and 

general area dose rates between 1.5 and 2 mrem/hr. The FSAR further indicated that neutron 

dose was one-sixth of the dose received from photon radiation (N:P = 0.166) (LMES 1997). 

Data from an area characterization study done along the outside boundary of the K1066E 

cylinder yard in 2000 indicated an N:P ratio of 0.274. This value was based on 9 locations that 

had positive neutron values out of a total of 86 sampling points (DOE ETTP 2000). 

N:P Ratio Data from Modeling Study

A modeling study for the neutron dose and N:P ratio from a typical array of large storage 

containers (14-t cylinders) of DU, NU, and LEU (5% enrichment) at the Oak Ridge K-25 

Gaseous Diffusion Plant can be found in Determination of Neutron to Gamma Dose Ratios for 

the UF6 Cylinder Yards (NISYS 2000). The array of tanks consisted of two rows of cylinders 

stacked 2 cylinders high and 25 cylinders long on a 6-inch thick concrete pad. Calculations of 

the neutron dose and N:P ratio were made at distances ranging from 1 meter to 300 meters at the 

mid-length of the array of tanks. These calculations considered the effects of radiation scattering 

by the 6-inch thick concrete pad and by air with a relative atmospheric humidity of 30%, 60%, 

and 90% (NISYS 2000). For tanks containing DU, NU, and LEU (5% enrichment), at 1 meter 

the N:P dose ratios were approximately 0.10, 0.22, and 0.88, respectively (NISYS 2000). The 

calculations at farther distances from the tanks containing DU, NU, and LEU (5% enrichment) 

were used to estimate bounding N:P ratios for radiation exposures at the tank yard of 

approximately 0.2, 0.4, and 1.5, respectively (NISYS 2000). 

N:P Ratio from Equipment and Area Monitoring Surveys

A summary of K-25 survey data was provided in 2015 by East Tennessee Technology Park

(ETTP) (previously known as the K-25 Site) personnel. The data cover the period January 1999 

through November 2006 (at which time the last of the UF6 cylinders were removed). Over 6,000 

paired neutron and photon survey data points were available that corresponded with equipment 

and general area measurements. Analysis of the equipment survey data yielded N:P ratio values 

of 0.099, 0.085, and 0.122 for distances on contact, 1 foot, and 1 meter, respectively. An N:P 

ratio of 0.605 ± 0.408 was calculated from 445 neutron/photon data points associated with 

general area measurements (Pope 2015).
White Paper Neutron Dose Assignment for K-25 and Portsmouth Gaseous 

Diffusion Plants

May 6, 2019

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This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

N:P Ratio Data from Employee Dosimetry Measurements (1989 to 2012)

In the past, dosimetry services for K-25 were provided by either the Oak Ridge National 

Laboratory (ORNL) or the Y-12 Plant. Therefore, to establish an N:P ratio, dosimetry record 

data for the Oak Ridge Gaseous Diffusion Plant (K-25), also known as ETTP, employees were 

extracted based on employee information and collated into a merged copy of the Y-12 Plant 

Dosimetry and ORNL Safety and Health Databases (dated February 6, 2013). Although the 

integration of the two databases resulted in a version containing a variety of different tables, only 

records extracted from Table 3, Individual_Dose_ETTP (hereafter referred to as Table 3 ETTP) 

were used, as the others did not have neutron dosimetry information, contained duplicate data, 

were limited to extremity dose, or contained only Portsmouth Gaseous Diffusion Plant records.

Evaluation of Table 3 ETTP

Table 3 ETTP initially contained a total of 187,295 records; dates ranged from January 1, 1989, 

through December 31, 2012. Duplicate data were removed, leaving only unique dosimetry 

records for K-25 employees during the period of interest. Also of note: 

• Personnel wore the Harshaw four-element beta/photon dosimeter and a separate fourelement neutron dosimeter.

• 129,132 unique photon/beta dosimeters remained after duplicates were removed.

• 16,701 unique neutron dosimeters remained after duplicates were removed.

• 11,599 individuals were monitored for photon/beta radiation from 1989 through 2012.

• 404 individuals were monitored for neutrons from 1989 through 2012.

• Approximately 3.5% of the individuals were monitored for beta/photon AND neutron 

radiation.

• The first positive neutron result occurred in 1993.

• Results from 369 neutron dosimeters were greater than or equal to the LOD.

• Neutron monitoring seldom occurred from 1990 through 1996 but seems to have been 

more frequent from 1999 through 2012.

Table 2 tabulates the number of photon/beta and neutron dosimeters exchanged for K-25 

employees by year.
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This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution. 

Table 2. K-25 annual photon and neutron badge exchanges 1989–2012. 

Year Photon/Beta Dosimeter 

Exchanges

Neutron 

Dosimeter Exchanges

Neutron Dosimeters 

(results > or = to the 

limit of detection)

1989 232 0 0

1990 401 7 0

1991 359 5 0

1992 550 2 0

1993 461 4 1

1994 327 3 0

1995 169 6 0

1996 253 12 0

1997 6,005 79 1

1998 6,304 59 0

1999 5,920 183 9

2000 5,980 773 20

2001 7,107 1,138 35

2002 7,002 1,415 11

2003 8,096 1,769 21

2004 10,239 1,923 26

2005 12,515 2,283 20

2006 10,637 2,030 25

2007 9,040 877 60

2008 8,137 959 44

2009 8,419 904 19

2010 8,618 857 54

2011 7,518 852 20

2012 4,843 561 3

Source: K-25_PORTS_Exposure Database

N:P Ratio Based on K-25 Dosimetry Data

A total of 369 records in Table 3 ETTP had individual neutron doses greater than or equal to the 

LOD of 10 mrem. An analysis of dosimeters with paired photon and neutron doses greater than 

the LOD was performed. The N:P ratio was calculated by dividing the neutron dose by the deep 

dose for each badge exchange. A ratio of 0.490 was calculated based on the average of the 

paired N:P ratios. Starting January 1, 2010, ORNL adopted the 1990 International Commission 

on Radiological Protection (ICRP) recommendations on neutron weighting factors (O’Connell 

2011). Based on this information, an N:P ratio of 0.420 was calculated. 
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This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

ADDITIONAL DATA ANALYSIS OF EMPLOYEE DATA MEASUREMENTS FOR 

K-25, PORTSMOUTH, AND THE Y-12 PLANT

An additional method of analysis was applied to the employee dosimetry datasets for K-25 and 

Portsmouth. This method – quantile regression – is discussed in ORAUT-RPRT-0087, 

Applications of Regression in External Dose Reconstruction (ORAUT 2018). In summary, this 

method uses quantile regression to fit a linear model to the neutron and photon doses (not an N:P 

ratio), giving the 50th- and 95th-percentile regression fits directly, with the added benefit of 

requiring no special treatment of data that might yield a traditional N:P ratio of 1. This approach 

also allows for exploratory data analysis, i.e., deriving fits for the 50th- and 95th-percentile 

exposed populations. 

The Y-12 Plant site profile discusses historical dosimetry information that can be used to 

determine neutron and photon exposure near HEU operations (ORAUT 2009). For this report, 

individual worker quarterly data for pairs of neutron and photon doses from workers in Y-12 

Plant Departments 2301 (Development Operations) and 2160 (Material Engineering) during the 

period from 1955 to 1959 were combined and used as a basis for obtaining an average N:P ratio. 

These data were selected because unique work activities involving EU were carried out in these 

departments during this period as indicated in Recycled Uranium Mass Balance Project Y-12 

National Security Complex (BWXT 2000). Excerpts from this report stated:

In the late 1950s, continuous solvent extraction equipment was installed in the B-1 

wing (of Building 9212). This period covered the transition from small-scale batch 

operations to the existing continuous recovery operation equipment in use today. 

The 9206 building has been used extensively over its lifetime for the chemical 

processing of uranium. Enriched uranium processes, activities, and/or missions of 

the 9206 Facility have included: conversion of UF6 to UF4 to uranium metal for 

weapons (1954 to 1964) and casting and machining of HEU metal for weapons 

(1955 to 1965). 

Film-badge data for Departments 2160 (Material Engineering) and 2301 (Project Design 

Development and Analytical Development) appear to be somewhat typical of the N:P ratio for 

workers who were exposed to neutrons from HEU sources in Buildings 9202, 9206, and 9212. 

The data analysis shown in Figure 3 is based on 89 paired neutron:photon results for 47 different 

workers in Departments 2160 and 2301. 

Table 3 provides the results of the quantile regression fits for K-25, Portsmouth, and Y-12 Plant 

and data for all three sites combined. In the case of K-25, the entire dataset from 1989 to 2012 

was used since the site was in a single (postproduction) mode during that era. The 50th- and 

95th-percentile regression fits for K-25 can be seen in Figure 1. At Portsmouth, enrichment 

activities ended in 2001, so the fits seen in Figure 2 are based on data from 1992 to 2001. Figure 

3 illustrates the fits for Y-12 Plant from 1955 to 1959. Finally, Figure 4 illustrates the fits for 

combining the datasets for all three sites. 
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Diffusion Plants

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This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution. 

Table 3. Summary of quantile regression fit parameters for K-25, Portsmouth, and Y-12 Plant 

employee data measurements. 

Site N 50th 

Percentile 

Slope

50th 

Percentile 

Intercept

(rem)

95th 

Percentile 

Slope

95th 

Percentile 

Intercept

(rem)

K-25 (1989–2012) 375 0.139 0.01 0.112 0.03

Portsmouth, Production 

Era (1992–2001)

3,727 0.133 0.002 0.231 0.004

Y-12 Plant (1955–1959) 89 0.14 0.03 0.7 0.1

K-25/Portsmouth/Y-12 

Plant Combined

4,191 0.195 0.002 0.846 0.002

The slope data for K-25, Portsmouth during the production era, and Y-12 Plant – especially at 

the 50th percentile – show good agreement. Please note that production of HEU product at 

Portsmouth ended in 1991; therefore, this production dataset represents work with mostly LEU 

product. 
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This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution. 

Figure 1. Quantile regression results for K-25 employee dosimetry data (1989–2012). 
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This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution. 

Figure 2. Quantile regression results for Portsmouth employee dosimetry data, 

production era (1992–2001). 
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Figure 3. Quantile regression results for Y-12 Plant employee dosimetry data (1955–

1959).
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Figure 4. Quantile regression results for the combined K-25, Y-12, and Portsmouth 

employee dosimetry data sets. (Data for K-25 are in red, data for Portsmouth are in 

blue, and data for Y-12 are in black). 

Additional Data for HEU Exposure 

Since the K-25 and Portsmouth data for exposure to HEU are limited, the following data from Y12 Plant are included here. A study was conducted in 1989 of neutron and photon emissions 

from small storage containers of HEU in Building 9212 at the Y-12 Plant in Oak Ridge, 

Tennessee (Soldat et al. 1990). At the time of the measurements, the storage area in Building 

9212 held small HEU containers of both UF4 and UO3. These small HEU containers were 

placed on a rack of shelves and arranged in a matrix that was criticality safe (Soldat et al. 1990). 

The exact enrichment value was not given, but the nature of the work in 9212 (as well as 

buildings 9202 and 9206 discussed below) would indicate an enrichment value of 90% or 

greater. The measurements were made at a height of 39 in. (1 m) above the floor and 27 in. (0.7 

m) from the nearest container. The location of the measurements was also selected so that it was

near only containers of UF4 (Soldat et al. 1990). The characterization of the neutron field 

consisted of measurements of the neutron energy spectrum and personal dose equivalent from 

both neutrons and photons. The measured values for the neutron dose rate ranged from 0.7 to 

2.08 mrem/hr. An N:P ratio was derived from this data by comparing the integrated neutron 

dose of 76.2 mrem for a period of 40.1 hours, as determined from measurements made with a 

tissue equivalent proportional counter, and the integrated photon dose of 68.0 mrem, as measured 

by phantom-mounted thermoluminescent dosimeters over the same time period. The resulting 

N:P ratio for these measurements was 1.12. 
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Table 4 summarizes N:P ratio data based on survey information from Y-12 Plant for the period 

1992 to 2004. The readings were taken either in general work areas or at a distance of 30 cm. 

Table 4. Summary of Y-12 N:P Plant ratio data, 1992–2004.

Date Building Room N:P Range N:P Average Reference

06/02/1992 9981/9998 G-2/G-5 0.13–1.0 0.37 Y-12 2013; SRDB Ref ID: 129045

02/28/2001 9212 D-107 0.06–0.50 0.2 Y-12 2013; SRDB Ref ID: 126485

07/11/2002 9212 1004 0.1–0.5 0.3 Y-12 2013; SRDB Ref ID: 128511

12/05/2003 9212 1004 0.25–1.0 0.6 Y-12 2013; SRDB Ref ID: 128511

12/08/2003 9212 1004 0.25–1.0 0.6 Y-12 2013; SRDB Ref ID: 128511

05/25/2004 9212 1014 0.22–0.43 0.31 Y-12 2013; SRDB Ref ID: 126498

GENERAL CONCLUSION

Tables 5 and 6 provide summaries of the neutron dose rate, photon dose rate, and N:P ratios data 

associated with K-25, Portsmouth, and Y-12 Plant operations that can be used to develop a 

neutron to photon ratio for assigning neutron doses for time periods at each facility (pre-1992 for 

K-25, pre-1996 for Portsmouth) when neutron dose data were either not reliable, not available, or 

not recorded. Although a wide range of survey, modeling, and static dosimetry data are available 

for all three sites, the quantile regression results from the personnel dosimetry measurements at 

each site would yield the most accurate N:P ratio result. In addition, good agreement was seen – 

especially at the 50th-percentile level – between the personnel measurement results from all 

three sites. 

The personnel data take into account the actual distances and residence time personnel would 

have had near potential source terms, whereas the survey data – by their nature – are static 

measurements taken during a snapshot of time. Survey data are typically taken at maximum 

dose rate locations to set bounds for radiological control purposes; thus, the survey data can be 

considered an upper bound. Most of the surveys indicate N:P ratios less than 0.4:1 with only 

three slightly greater than 1.2:1. This further confirms that the 2:1 upper bound N:P ratio 

discussed in the DOE Guide of Good Practices for Occupational Radiological Protection in 

Uranium Facilities (DOE 2009) is indeed a conservative upper bound. Given multiple work 

locations and personnel movement between areas of neutron exposure with N:P ratios less than 

0.4 – and areas of no neutron exposure – the data resulting from the quantile regression analysis 

of personnel dosimetry provide the best estimate for an overall N:P ratio for unmonitored 

workers. 

An N:P relationship based on the quantile regression analysis of dosimetry data for all three sites 

combined – as summarized in Tables 3 and 6 – is recommended for assigning neutron dose for 

unmonitored workers in eras as described above. Application of the guidance in Appendix A 

yields a lognormal distribution that reflects the 50th- and 95th-percentile fits for the quantile 

regression analysis of the personnel dosimetry data from K-25, Portsmouth, and the Y-12 Plant 

combined. This distribution is to be combined with photon dose (defined as a constant or 

distribution) – using Monte Carlo methods as needed – to yield a distribution of neutron dose. 
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Table 5. Summary of neutron dose rates, photon dose rates, and N:P ratios associated with natural, 

depleted, and enriched uranium materials at Paducah, Portsmouth, and K-25 Gaseous Diffusion Plants and 

the Y-12 Plant.

Location/Reference Material

Neutron Dose 

Rate (mrem/hr)

Photon Dose 

Rate (mrem/hr) N:P Ratio

DOE Good Practices Guide (DOE 

2009)

NU to 5% 

EU

0.01-0.2 NAa 2:1

DOE Good Practices Guide (DOE 

2009)

97% HEU 2-4 (contact)

1-2 (1 m)

NA 2:1

Paducah GDP, Cylinder Storage 

Yard (BJC 1999)

DU, NU NA NA 0.2

Portsmouth GDP (Cardarelli 1997) HEU 3 (contact) NA 0.125

Portsmouth GDP (Cardarelli 1997) NU, EU, 

HEU

<0.5 (1 m) NA 0.125

Portsmouth GDP, X-326, Full 5” 

Cylinders (Bassett 1986)

97% HEU ≤3.0 (surface) ≤2.4 (surface) 1.25

Portsmouth Area Monitoring 

Results (McGuire 2008)

DU, NU, 

LEU, HEU NA NA

0.147 (avg)

0.01 (min)

0.398 (max)

K-25 GDP, Cylinder Storage Yard 

(NISYS 2000)

DU 0.07 (1 m) 0.70 (1 m) 0.10 (1 m)

K-25 GDP, Cylinder Storage Yard 

(NISYS 2000)

NU 0.15 (1 m) 0.68 (1 m) 0.22 (1 m)

K-25 GDP, Cylinder Storage Yard 

(NISYS 2000)

5% LEU 0.60 (1 m) 0.68 (1 m) 0.88 (1 m)

K-25, FSAR (LMES 1997) DU, NU, 

LEU, HEU

1.5-6 (contact)

1.5-2 (general 

area)

1.5-6 (contact)

1.5-2 (general 

area)

0.166

K-25 Equipment and Area 

Monitoring Surveys (Pope 2015) DU, NU, 

LEU, HEU

NA NA 0.099 (contact)

0.085 (1 ft)

0.122 (1 m)

0.605 (general area)

Y-12 Plant, Bldg. 9212 (Soldat, et 

al., 1990)

HEU 1.9 1.7 1.12

Y-12 Plant, Bldg. 9981, 9998, and 

9212

(Y-12 1992, pp. 4-7)

(Y-12 2001, p. 4)

(Y-12 2003, p. 18)

(Y-12 2003, p. 6)

(Y-12 2003, p. 4)

(Y-12 2004, p. 4)

HEU

2–32

1–1.8

0.4–8 

0.1–0.4

0.1–0.5

1.4–1.8

1–4 

0.1–0.5

0.2–0.4

0.1

0.1

0.4–0.6

0.37 (1 ft)

0.2 (1 ft)

0.3 (1 ft)

0.6 (1 ft)

0.6 (1 ft)

0.31 (1 ft)

a. NA = not applicable. 
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Table 6. Summary of N:P ratios and quantile regression relationships associated with natural, depleted, and 

enriched uranium materials at Portsmouth, K-25, and Y-12 Plants, based on personnel dosimetry.

Location Material

N:P 

Ratio Quantile Regression Relationship

K-25 Personnel Dosimetry, 

1989–2012

DU, NU, 

LEU, HEU

0.420 50th neutron = 0.139 [photon (rem)] + 0.01 (rem)

95th neutron = 0.112 [photon (rem)] + 0.03 (rem)

Portsmouth Personnel 

Dosimetry, 1992–2013

DU, NU, 

LEU, HEU

0.369 50th neutron = 0.133 [photon (rem)] + 0.002 (rem)

95th neutron = 0.231 [photon (rem)] + 0.004 (rem)

Y-12 Plant Personnel 

Dosimetry, 1955–1959

HEU NAa 50th neutron = 0.14 [photon (rem)] + 0.025 (rem)

95th neutron = 0.7 [photon (rem)] + 0.098 (rem)

K-25/Portsmouth/Y-12 

Plant Combined

DU, NU, 

LEU, HEU

NAa 50th neutron = 0.195 [photon (rem)] + 0.002 (rem)

95th neutron = 0.846 [photon (rem)] + 0.002 (rem)

a. NA = not applicable. 
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REFERENCES

Bassett, A. C., 1986, External Dose Rates from Five-Inch Product Cylinders, Portsmouth 

Gaseous Diffusion Plant, Goodyear Atomic Corporation, Piketon, Ohio, February 17. 

[SRDB Ref ID: 23926] 

BJC (Bechtel Jacobs Company), 1999, Paducah UF6 Cylinder Painting Project Neutron Dose 

Study, Paducah Gaseous Diffusion Plant, Paducah, Kentucky, July 7. [SRDB Ref ID: 

13682] 

BJC (Bechtel Jacobs Company), 2000, Evaluation of Potential Radiation Doses to Members of 

the Public and ETTP Unmonitored Site Workers East Tennessee Technology Park, Oak 

Ridge, Tennessee, BJC OR-585/R1, Oak Ridge, Tennessee, May 1. [SRDB Ref ID: 

29760] 

BWXT Y-12, 2000, Recycled Uranium Mass Balance Project Y-12 National Security Complex 

Site Report, Y/LB-16,036, Rev.1, Y-12 National Security Complex, Oak Ridge, 

Tennessee, December. [SRDB Ref ID: 16500] 

Cardarelli, J. J., II, 1997, NIOSH Health Hazard Evaluation Report, HETA 96-0198-2651,

Portsmouth Gaseous Diffusion Plant, Piketon, Ohio, National Institute for Occupational 

Safety and Health, Cincinnati, Ohio. [SRDB Ref ID: 10913] 

DOE (U.S. Department of Energy), 2009, Guide of Good Practices for Occupational 

Radiological Protection in Uranium Facilities, DOE-STD-1136-2009, Washington, D.C., 

July. [SRDB Ref ID: 97381] 

DOE ETTP (U.S. Department of Energy, East Tennessee Technology Park), 2000, Area 

Characterization Survey, Oak Ridge, Tennessee, February 15. [SRDB Ref ID: 93592] 

LMES (Lockheed Martin Energy Systems), 1997, K-25 Site UF6 Cylinder Storage Yards Final 

Safety Analysis Report, K/D-SAR-29, Oak Ridge, Tennessee, February 28. [SRDB Ref 

ID: 126947] 

McGuire M., 2008, Area Monitor TLD Results, memorandum from Marsha McGuire, 

Portsmouth Gaseous Diffusion Plant, United States Enrichment Corporation (USEC), 

Piketon, Ohio, August 11. [SRDB Ref ID: 131566] 

NISYS (NISYS Corporation), 2000, Determination of Neutron to Gamma Dose Ratios for the 

UF6 Cylinder Yards, Calc. No. 1073-018-C001, Rev. 0, Duluth, Georgia, August 25. 

[SRDB Ref ID: 108666] 
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positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution. 

O’Connell, P., 2011, DOE Adoption of 1990 ICRP Recommendations on Neutron Weighting 

Factors, email from Peter O’Connell, U.S. Department of Energy, Washington, D.C., 

December 20. [SRDB Ref ID: 106069].

ORAUT (Oak Ridge Associated Universities Team), 2009, Y-12 National Security Complex – 

Occupational External Dosimetry, ORAUT-TKBS-0014-6, Rev. 02, Oak Ridge, 

Tennessee, December 18. [SRDB Ref ID: 77701].

ORAUT (Oak Ridge Associated Universities Team), 2018, Applications of Regression in 

External Dose Reconstruction, ORAUT-RPRT-0087, Rev. 00, Oak Ridge Tennessee, 

March 13. [SRDB Ref ID: 170100] 

Pope, J., 2015, Spreadsheet of Neutron and Photon Dose Rates at K-25, Equipment and General 

Area Surveys, East Tennessee Technology Park/URS and CH2M Oak Ridge LLC 

(UCOR), Oak Ridge, Tennessee, May 15. [SRDB Ref ID: 144768] 

PGDP (Portsmouth Gaseous Diffusion Plant), 2002, Dosimetry Program Standards 1995-2002, 

UE2-HP-RP1034, Piketon, Ohio, 2002. [SRDB Ref ID: 75434] 

PGDP (Portsmouth Gaseous Diffusion Plant), date unknown, Unredacted Electronic Version of 

Health Physics Records System, Piketon, Ohio. [SRDB Ref ID: 138026] 

Scherpelz, R. I. and M. K. Murphy, 1995, Enriched Uranium Cylinder Neutron Characterization 

Measurements at the Portsmouth Gaseous Diffusion Plant, Pacific Northwest Laboratory, 

Richland, Washington, September. [SRDB Ref ID: 109074] 

Soldat, K. L., L. W. Brackenbush, M. P. Moeller, R. I. Sherpelz, and J. E. Tanner, 1990, Neutron 

Dose Equivalent and Energy Spectra Measurements at the Oak Ridge National 

Laboratory and Y-12 Plant, PNL-7528, Pacific Northwest Laboratory, Richland, 

Washington. [SRDB Ref ID: 11093] 

Soldat, K. L. and J. E. Tanner, 1992, Neutron Dose Equivalent and Energy Spectra 

Measurements at the Portsmouth Gaseous Diffusion Plant, Pacific Northwest Laboratory, 

Richland, Washington, April. [SRDB Ref ID: 8119] 

Y-12, 1992, Health Physics Survey for Uranium Surface Contamination Forms June 1992, Y-12 

Plant, Oak Ridge, Tennessee. [SRDB Ref ID: 129045] 

Y-12, 2001, Radiation and Neutron Surveys of Specific Cans in Building 9212 February 28, 

2001, Y-12 Plant, Oak Ridge, Tennessee. [SRDB Ref ID: 126485] 
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ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

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information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution. 

Y-12, 2003, RAD CON Organization Monitoring and Survey Results February - December 

2003, Y-12 Plant, Oak Ridge, Tennessee. [SRDB Ref ID: 128511] 

Y-12, 2004, Radiological Control Organization Monitoring and Survey Results of Building 9212 

for Gamma and Neutron March and May 2004, Y-12 Plant, Oak Ridge, 

Tennessee. [SRDB Ref ID: 126498] 
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APPENDIX A: QUANTILE REGRESSION ANALYSIS IMPLEMENTATION WITHIN

INTERACTIVE RADIOEPIDEMIOLOGICAL PROGRAM (IREP) 

Using a quantile regression analysis of paired photon/neutron data, an N:P ratio can be derived 

for calculating neutron dose based on photon dose using the following inputs (note that this N:P 

ratio derivation is needed to implement the quantile regression results in the calculation tools 

used by ORAUT): 

1. 50th-percentile equation

2. 95th-percentile equation

3. Known photon dose (normal or lognormal distribution) 

The neutron dose at any photon dose is assumed to have a lognormal distribution, the parameters 

of which are described by the 50th- and 95th-percentile equations. 

In this discussion, N50(p) denotes the 50th-percentile neutron dose for a given photon dose p and 

N95(p) denotes the 95th-percentile neutron dose for a given photon dose (p). 

The lognormal parameters for the N:P ratio of a given photon dose are: 

(A-1) 50 ( ) ( ) ( )

N p GM p

p =

where

z95 = 1.64485 (normal standard deviation for the 95th-percentile)

and

(A-2) 

95

50

95

( ) ln ( )

( )

N p

N p

z

GSD p e

            =

To obtain the neutron dose, the derived N:P ratio is multiplied by the photon dose distribution 

(see example calculation). 

Example Calculation

N:P ratio from quantile regression relationship from K-25/Portsmouth/Y-12 Plant combined: 

N95(p) = 0.846 p + 0.002

N50(p) = 0.195 p + 0.002

Photon dose p = 0.05 rem 
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Calculation of N:P Ratio from Photon Dose and Quantile Regression Neutron Dose 

(A-3) 0.011366 ( ) 0.22732

0.05 GM p = =

and

(A-4)

0.0444575 ln 0.011366

1.64485 GSD p e ( ) 2.291481

       

  = =

Monte Carlo Simulation to Assign Neutron Dose 

Photon dose (p) = 0.05 rem ± 0.015 rem (normal distribution) 

N:P ratio: Geometric Mean (GM) = 0.22732, Geometric Standard Deviation (GSD) = 2.291481 

(lognormal distribution)

A sample from the normal photon dose distribution is multiplied by a sample from the derived 

N:P ratio. This process is repeated for 10,000 iterations and a distribution is fit to the resulting 

data set (see results in Figure A-1). 
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Figure A-1. Lognormal distribution fit of calculated neutron data based on photon sample and N:P ratio 

sample. Neutron dose lognormal fit from photon sample: 0.05 ± 0.015 rem. (The parameters for this fitted 

lognormal are mean = -4.3072 rem and standard deviation = 0.73716, and for use with IREP, GM = 0.0135 

rem, GSD = 2.090, and shift = -0.0019819).